Buggy code:
public class IMAPProtocol { public static final int DEFAULT_PORT = 143 ; private static final byte [ ] CRLF = new byte [ ] { ( ( byte ) ( '\r' ) ) , ( ( byte ) ( '\n' ) ) } ; private Socket socket ; private IMAPInputStream in ; private DataOutputStream out ; private ArgumentWriter argumentWriter ; public String answer ; private String userId = new String ( "A" ) ; private int id = 0 ; private String idString ; private String result ; public IMAPProtocol ( ) { } public boolean openPort ( String host ) throws IOException { } public boolean openPort ( String host , int port ) throws IOException { } protected String generateIdentifier ( ) { } public DataOutputStream getOutputStream ( ) { } public String sendString ( String s , Arguments args ) throws Exception { } public IMAPResponse getResponse ( WorkerStatusController worker ) throws Exception { } protected synchronized IMAPResponse [ ] sendCommand ( String command , Arguments args ) throws Exception { } protected synchronized IMAPResponse [ ] sendCommand ( String command , Arguments args , WorkerStatusController worker ) throws Exception { } protected synchronized IMAPResponse [ ] sendCommand ( String command , Arguments args , int count , WorkerStatusController worker ) throws Exception { } protected synchronized void sendSimpleCommand ( String command , Arguments args ) throws Exception { } public void handleResult ( IMAPResponse response ) throws Exception { } protected void notifyResponseHandler ( IMAPResponse [ ] responses ) { } protected void handleResponse ( IMAPResponse r ) { } public void login ( String user , String password ) throws Exception { } public IMAPResponse [ ] select ( String mailbox ) throws Exception { } public IMAPResponse [ ] fetchList ( String cmd , String reference , String pattern ) throws Exception { } public IMAPResponse [ ] lsub ( String reference , String pattern ) throws Exception { } public IMAPResponse [ ] list ( String reference , String pattern ) throws Exception { } public void create ( String mailbox ) throws Exception { } public void delete ( String mailbox ) throws Exception { } public void rename ( String oldMailbox , String newMailbox ) throws Exception { } public void subscribe ( String oldMailbox ) throws Exception { } public void unsubscribe ( String oldMailbox ) throws Exception { } public void append ( String mailBox , String messageSource ) throws Exception { } public IMAPResponse [ ] fetch ( String item , String messageSet , boolean uid ) throws Exception { } public IMAPResponse [ ] fetch ( String item , String messageSet , boolean uid , WorkerStatusController worker ) throws Exception { } public IMAPResponse [ ] fetch ( String item , String messageSet , boolean uid , int count , WorkerStatusController worker ) throws Exception { } public IMAPResponse [ ] fetchUIDList ( String messageSet , int count , WorkerStatusController worker ) throws Exception { } public IMAPResponse [ ] fetchFlagsList ( String messageSet , int count , WorkerStatusController worker ) throws Exception { } public IMAPResponse [ ] fetchHeaderList ( String messageSet , String headerFields ) throws Exception { } public IMAPResponse [ ] fetchMimePartTree ( String messageSet ) throws Exception { } public IMAPResponse [ ] fetchMimePart ( String messageSet , Integer [ ] address , WorkerStatusController worker ) throws Exception { } public IMAPResponse [ ] fetchMessageSource ( String messageSet , WorkerStatusController worker ) throws Exception { } public IMAPResponse [ ] storeFlags ( String messageSet , String flags , boolean enable ) throws Exception { } public IMAPResponse [ ] removeFlags ( String messageSet , String flags , boolean enable ) throws Exception { } public IMAPResponse [ ] expunge ( ) throws Exception { } public IMAPResponse [ ] search ( Arguments args ) throws Exception { } public IMAPResponse [ ] searchWithCharsetSupport ( String charset , Arguments args ) throws Exception { } public IMAPResponse [ ] search ( String messageSet , Arguments args ) throws Exception { } public IMAPResponse [ ] copy ( String messageSet , String mailbox ) throws Exception { Arguments args = new Arguments ( ) ; <START_BUG> args . add ( messageSet ) ; <END_BUG> args . add ( mailbox ) ; IMAPResponse [ ] responses = sendCommand ( "UID<seq2seq4repair_space>COPY" , args ) ; notifyResponseHandler ( responses ) ; IMAPResponse r = responses [ ( ( responses . length ) - 1 ) ] ; handleResult ( r ) ; return responses ; } }

Fix:
args . add ( new Atom ( messageSet ) ) ;